Pneumatic tires can be very efficient. Their relatively thin, solid structure, combined with an air volume, suffers low losses due to hysteresis while conforming to the shape of the ground to gain traction and grip. However, pneumatic tires also have disadvantages in that they are vulnerable to impacts and damage that can cause the tire to lose air.
For example, conventional clincher bicycle tires traditionally use an inner tube that is separate from the tire to retain the air. In such a structure, the tire is mounted on the rim of the bicycle wheel with the inner tube placed inside of the inner casing of the tire. The tire is inflated by filling the inner tube with air and the inner tube fills the tire casing entirely.
A conventional inner tube structure is vulnerable to different types of punctures, such as “pinch” and “piercing” punctures. In a “pinch” puncture, the tire may strike an obstacle (e.g., a rock, a curb, a ledge) such that the tire is compressed toward the rim of the wheel. When the tire compresses, the inner tube is pinched between the tire casing and the edge of the rim of the wheel upon which the tire is mounted, which may add a significant amount of stress to the inner tube. Additionally, upon striking the obstacle, the inner tube may be nipped against the hard edge created by the rim and the obstacle. In this situation the tube may be stretched beyond its elastic limit, typically creating two holes in the tube which then allow the air inside the tube to escape rapidly.
In a “piercing” puncture, a sharp object passes through both the tire and tube to create a hole that allows the air to escape from the tube. Piercing punctures may be addressed by the addition of a liquid sealant to the inner tube that can block many smaller holes. However, in a traditional inner tube system, the sealant effectiveness may be reduced because the tube may move relative to the tire casing while a sharp object is still embedded in the tire casing, thus, reopening the hole in the tube or creating new holes in the tube. A sealant set-up with an inner tube may also add more weight to a wheel that already has extra weight due to the presence of an inner tube and a tire.
Further, inner-tube systems may increase the likelihood of damaging the valve stem used to inflate the tube. For example, forces exerted on the tire may cause the tire to rotate, which in turn may cause the tube to rotate with respect to the rim. In such instances, the valve stem of the tube that is passing through a hole in the rim may become damaged due to the rotation of the tube.
An alternative system for holding air in a clincher tire is the “tubeless” method. In a tubeless system, the bead of the tire may seal against the rim to hold air inside of the tire without the use of an inner tube. A tubeless system is much less vulnerable to “pinch” punctures as there is no separate tube to pinch, and piercing punctures can also be largely addressed by the addition of a liquid sealant to the tire which can block many smaller holes. The additional weight of the sealant may be less worrisome due to any additional weight associated with an inner tube being removed. Additionally, the sealant may be more effective in a tubeless tire because the puncturing object may not create more than the original hole in the tire.
However, the tubeless systems currently in use also have problems. For example, although tubeless systems are effectively immune to pinch punctures associated with inner-tube systems, an impact that might normally cause a pinch puncture in an inner-tube system may be capable of pushing the bead of the tubeless tire away from the rim, allowing for a sudden loss of air. Additionally in some instances (e.g., with lower pressures that may be desirable in some applications such as off-road use), there is also a risk of an impact damaging the sidewall of the rim. Once the rim is damaged in a tubeless system, the seal at this junction is also likely to be compromised such that air may escape. Additionally, in some instances under heavy cornering loads (e.g., with low pressures), the sidewall of the tire may be forced away from the rim, allowing for a sudden loss of air.
Further, to achieve the desired tight fit of a tubeless system, special tires and rims may be required to achieve a tight fit between the rim and the tire bead to try to maintain a good seal and to increase the force required to separate the bead of the tire from the rim's sidewall, to reduce the likelihood of the air escaping. While this may be effective, it can make the seating of the tire onto the rim much more difficult and it is still relatively common to encounter a situation in which the side loads pull the rim bead away from the tire, allowing the air from inflation to escape.
Another drawback with tubeless designs is that inflation can be difficult since air tends to leak until the tire bead is fully seated and held in place against the rim by air pressure. Typically, a supply of air is required at a rate that is not easily achieved outside of a workshop (e.g., during a repair by the user at the road or trail side). Without a sufficiently rapid supply of air, quickly pushing the tire out and into position in order to create a seal can be very difficult to achieve. This means that many riders may feel the need to carry an inner-tube or tubes as a reliable means of re-inflating a deflated tire at the side of the bicycle trail, should it be necessary.
Yet another problem with tubeless tires is that the seal at the rim often leaks slightly. Sealant is somewhat effective at eliminating these leaks, but there is still flexure of the tire that occurs during use because this junction is subject to movement. Since the tire is sealed over a relatively small area, and it is not firmly held closed, it is common for it to re-open and begin to leak slowly again. Damage to the rim from impacts can magnify this problem significantly.
The typical tubeless system has yet another issue in that it can be difficult to move the wheel to a position in which sealant lies against the bead and rim joint in order to seal such leaks. With a large volume tire, laying the wheel on its side causes the sealant to sit in the tumblehome (side curve) of the tire, rather than against the bead-rim interface. It is typically necessary to manually shake the wheel in order to “slosh” the sealant up to the leaking bead-rim interface, and this method is commonly demonstrated by sealant manufacturers. This procedure is laborious and time consuming and requires some skill from the user to complete it successfully. It also requires the removal of the wheel from the bicycle to perform the task, which also adds an inconvenience.